A nasal cannula is a medical device that may be used to deliver supplemental oxygen to a person in certain medical situations. The nasal cannula may include a tube that at one end splits into two prongs, the two prongs being placed in the nostrils. The other end of the tube may be connected to an oxygen supply. In some cases, a nasal cannula may be used to measure respiratory gases. Capnography is the monitoring of the concentration or partial pressure of carbon dioxide (CO2) in the respiratory gases. Capnography may be used as a monitoring tool during anesthesia and intensive care.
Capnography may be presented as a capnogram, a graph of expiratory CO2 plotted against time. A typical capnogram for patients is characterized by a set of specific elements. Typically, a capnogram is divided into 4 distinct phases. In phase I, the CO2 concentration starts at zero, used as a respiratory baseline, typically 0 millimeters of mercury (mmHg). Phase II indicates the sharp expiratory upstroke of expired CO2 as alveolar gas exits the airway. The sharp rise in expired CO2 levels out in phase III, resulting in a maximum CO2 concentration being reached. This maximum CO2 concentration is referred to as end-tidal CO2 (ETCO2). With the start of inhalation during phase IV, the CO2 concentration decreases to zero (i.e., 0 mmHg) as atmospheric air again enters the airway. The amplitude of the capnogram depends on the ETCO2 concentration and the width depends on the expiratory time. A characteristic shape exists for all subjects with normal lung function. Accordingly, advancements in capnography enables an anesthesiologist to monitor a patient's vital signs more reliably. Nevertheless, benefits may be realized by providing systems and methods for improving capnography systems.